The instant invention relates to compositions primarily suitable for dental and medical restoration; i.e., dental filings or dental and bone adhesive, and to the method of their use for such purposes and methods of manufacture.
There have been repeated efforts to replace amalgam as a filling in dental practice, as well as to have suitable adhesives for dental purposes other than for fillings. One polymeric material that has been suggested for such use is bis-glycidlymethylmethacrylate polymer bis-GMA). When used as a dental adhesive or filling, together with the other usual components admixed therewith, such bis-GMA offers good mechanical and physical properties, but exhibits considerable post-shrinkage and relatively poor adhesion to bone substrate. Thus, it is not entirely satisfactory for use as an adhesive in dental work or as a filling. The use of such GMA material is disclosed in U.S. Pat Nos. 4,588,756 and 4,964,911.
Zero polymerization shrinkage is one of the most necessary features of a dental restorative so that accumulated stresses do not debond the dentin-restorative interface which can result in leakage and microbial attack.
U.S. Pat. No. 4,659,751 discusses the use of a variety of acids and other materials in order to treat the surface of teeth, such as enamel and dentin, to activate the surfaces for improved adhesion to polymers, but no disclosure or suggestion is made therein of the use of the GMA of bis-GMA.
In this regard, it is well known that in order to achieve desired bonding on enamel or dentin, the protein coatings on the enamel and the smear level on dentin must be removed. Traditionally, this has been done utilizing organic acids such as phosphoric, citric, and lactic acids, as well as ethylene diamine dicarboxylic acid. Accordingly, many of the new products provide such polyacids as surface cleaning and priming agents for enamel and dentin. At the present time bis-GMA resins themselves are not inherently adhesive to tooth surfaces, and if used acid etching is required.
Nematic liquid crystals are known which can be photopolymerized at high temperature, i.e., 90xc2x0 C., within seconds with very low polymerization shrinkage to densely crosslinked networks of reaction extent greater than 95% by the usual free radical methods. The low polymerization shrinkage for such compounds originates from the high packing efficiency that already exists in the nematic state, thus minimizing the entropy reduction that occurs during polymerization.
However, polymerization at lower temperatures, such as room temperature, results in undesirable intervening smectic and crystalline phases making them unsuitable as photopolymerized medical and dental restoratives.
The foregoing problems and deficiencies of the prior art are overcome by the instant invention which provides especially low (essentially zero) polymerization shrinkage in the matrix resin while permitting high loading of strengthening materials and high matrix molecular weight, and yet permitting the matrix to strain soften, and flow onto and/or into areas to be cemented or restored, such as bone and tooth crevices, and be polymerized at room temperature.
Briefly, the present invention comprises novel transparent or translucent acrylate (or methacrylate) based matrix-metal oxide compositions, metal oxide nanoparticles with surface complexes, mixed particles formed by such nanoparticles with larger monosized silica particles to improve mechanical strength, and photopolymerizable room temperature nematics that have high strength and hardness with essentially zero shrinkage.
The invention also comprises the methods hereinafter set forth for making such tantalum oxide-silica microparticles, for making composites having reduced particle surface acidity, and the method of dental and bone restoration using the noted composites.